Stringent emission standards for internal combustion engines suggest the use of advanced fuel metering techniques that provide extremely small fuel droplets. The fine atomization of the fuel not only improves emission quality of the exhaust, but also improves the cold weather start capabilities, fuel consumption and performance. Typically, optimization of the droplet sizes dependent upon the pressure of the fuel, and requires high pressure delivery at roughly 7 to 10 MPa. However, a higher fuel delivery pressure causes greater dissipation of the fuel within the cylinder, and propagates the fuel further outward away from the injector nozzle. This propagation makes it more likely that the fuel spray will condense on the walls of the cylinder and the top surface of the piston, which decreases the efficiency of the combustion and increases emissions.
To address these problems, a fuel injection system has been proposed which utilizes low pressure fuel, define herein as generally less than 4 MPa, while at the same time providing sufficient atomization of the fuel. One exemplary system is found in U.S. Pat. No. 6,712,037, commonly owned by the Assignee of the present invention, the disclosure of which is hereby incorporated by reference in its entirety. Generally, such low pressure fuel injectors employ sharp edges at the nozzle orifice for atomization and acceleration of the fuel. However, the relatively low pressure of the fuel and the sharp edges result in the spray being difficult to direct and reduces the range of the spray. More particularly, the spray angle or cone angle produced by the nozzle is somewhat more narrow. At the same time, additional improvement to the atomization of the low pressure fuel would only serve to increase the efficiency and operation of the engine and fuel injector.
Accordingly, there exists a need to provide a fuel injector having a nozzle design capable of sufficiently injecting low pressure fuel while increasing the control and size of the spray angle, as well as enhancing the atomization of the fuel.